1. Field of the Invention
The present invention relates to improved methods of completing wells in unconsolidated subterranean zones, and more particularly, to improved methods of completing such wells whereby the migration of sand with the fluids produced therefrom is prevented.
2. Description of the Prior Art
Oil and gas wells are often completed in unconsolidated formations containing loose and incompetent sand which migrates with fluids produced by the wells. The presence of formation sand in the produced fluids is disadvantageous and undesirable in that the particles abrade pumping and other producing equipment and reduce the fluid production capabilities of producing zones in the wells. Heretofore, unconsolidated subterranean producing zones have been completed by forming gravel packs in the well bore adjacent the producing zones. The gravel packs serve as filters and function to prevent formation sand from migrating with produced fluids into the well bores.
In a typical gravel pack completion, a screen is placed in the well bore and positioned within the unconsolidated subterranean producing zone which is to be completed. The screen is typically connected to a tool which includes a production packer and a crossover, and the tools is in turn connected to a work or production string. A particulate material which is usually graded sand, often referred to in the art as gravel, is pumped in a slurry down the work or production string and through the crossover whereby it flows into the annulus between the screen and the well bore. The liquid forming the slurry leaks off into the subterranean zone and/or through the screen which is sized to prevent the particulate material in the slurry from flowing therethrough. As a result, the particulate material is deposited in the annulus around the screen whereby it forms a gravel pack. The size of the particulate material in the gravel pack is selected such that it prevents formation sand from flowing into the well bore with produced fluids.
A problem which is often encountered in forming gravel packs, particularly gravel packs in long and/or deviated unconsolidated producing zones, is the formation of particulate material bridges in the annulus. That is, non-uniform packing of the particulate material in the annulus between the screen and the well bore often occurs as a result of the loss of carrier liquid into high permeability portions of the subterranean zone. This, in turn, causes the formation of particulate material bridges in the annulus before all of the particulate material has been placed. The particulate material bridges block further flow of the slurry through the annulus which leaves voids below the bridges. When the well is placed on production, the flow of produced fluids is concentrated through the voids in the gravel pack which soon causes the screen to be eroded and the migration of formation sand with the produced fluids to result.
Thus, there are needs for improved methods of completing wells utilizing gravel packs whereby voids in the gravel packs do not occur or are eliminated prior to when the wells are placed on production.